Electronic devices, such as microprocessors, are tested during and after manufacturing to ensure that performance, quality and reliability requirements are met. Missing parts, malfunctioning components, incomplete soldering, incomplete traces of conductive material and cosmetic problems, for example, may be found. Units failing the test may be repaired or discarded.
Automated testing is commonly used in the high volume manufacturing of electronic components, such as microprocessors. FIG. 1 is a schematic representation of a common test system 10 including a tester 12 containing a handler 14, a test interface unit (“TIU”) 16, a docking station 18 and a device under test (“DUT”) 20. A test contactor 23 supports contacts 24 that electrically couple contacts on the DUT 20 to the TIU 16. The test contactor typically has a plastic housing. The handler 14 automatically loads the DUT onto the contacts 24 of the test contactor 23 and removes the DUT 20 when the test is completed. Here, the DUT 20 is a microprocessor for a wireless device and the contacts of the DUT 20 are in the form of a ball grid array (BGA) 25. The TIU 16 is a printed circuit board (“PCB”) that electrically couples the DUT 20 to test circuitry, here, the tester 12. The TIU 16 typically comprises electrical channels (microstrips) and electronic devices such as capacitors. The TIU 16 is supported on the docking station 18. Under software control, the tester 12 provides signals to the DUT 20 and evaluates the signals generated by the DUT 20 in response to the test signals, to determine whether the DUT 20 is operating properly, as is known in the art. Multiple DUTs 20 may be simultaneously evaluated in the Tester 12.
Electromagnetic emissions from the DUT 20 and traces on the TIU 16 may cause electromagnetic interference (“EMI”) that can corrupt the signals on the TIU 16, preventing analysis of the results. EMI can be a particularly serious problem with electronic components, such as microprocessors, for use in wireless devices. To shield the DUT 20, a thick aluminum plate 26 is provided over the TIU 16. The plate covers about three fourths (¾) of the area of the TIU 16 and has openings over the test contactor 23 to receive the DUTs 20. One such opening for receiving one DUT 20 is shown in FIG. 1. Exemplary paths 27 of electromagnetic flux 28 emitted by the DUT 20 are shown in FIG. 1. Only a small portion of the flux lines are intercepted by the aluminum plate 26. The unscreened flux may interfere with the signals received from and returned to the TIU 16, as well as with other DUTs being tested. Since the housing of the test contactor 24 is typically a plastic, non-conductive material, electromagnetic flux from the environment could also penetrate the housing and interfere with the test signals. For example, electromagnetic flux that may interfere with testing may be emitted by cellular phones, by nearby airports and by other equipment on the test floor. In addition, the removal and installation of the aluminum plate 26 is cumbersome and delays the testing process.
An improved shielding system that more effectively blocks EMI during testing would be advantageous.